If you need to make an installation boot disk for OS X you're in the right place!
Whatever your feelings are about the "download only" delivery method Apple imposes for its operating system updates you would be well advised to ensure you have a bootable version of the OS for future emergency use. Especially important as the installer automatically deletes itself once it has installed meaning another huge download if you need to reinstall.
By far the easiest way to create a bootable installation disk for OS X is using DiskMaker X from http://diskmakerx.com/. DiskMaker X is a free app created with AppleScript that can be used to create a bootable install disk.
Over the last few years each time a new version of OS X is released I created a tutorial for how to create a boot disk from the file the Mac App Store downloads to your system.
Here are direct links to each of the tutorials: